In recent years, the need for a low-sulfur heavy oil has been increasing for preventing environmental pollution problems such as acid rain. On the other hand, as crude oil has become heavy globally, there is an increasing tendency of crude oil containing large amounts of sulfur, asphaltene, heavy metals and the like needing to be treated, and the conditions for hydrogenating heavy hydrocarbon oil such as atmospheric distillation residual oil or vacuum distillation residual oil to obtain a low-sulfur heavy oil have been getting severer. The prolonged demand structure involving a shortage of middle distillates is also a background to this tendency.
As a result, improvements in activity and life of a hydrogenation catalyst have been studied intensively for the purpose of increasing production of a low-sulfur heavy oil by hydrogenating heavy hydrocarbon oil. For example, a hydrogenation catalyst is disclosed in which the catalyst average pore diameter is improved by supporting an active metal on an inorganic oxide carrier containing alumina and zinc without reducing the strength of the catalyst (for example, refer to PTL 1).
On the other hand, heavy hydrocarbon oil is required to have improved storage stability. Hydrogenated heavy hydrocarbon oil is stored under heating to maintain fluidity until shipping in consideration of workability at the time of shipping. In addition, the oil may be stored for a long period of time after the oil is shipped as a product before use. Therefore, depending on a thermal history and the atmosphere at the time of storage, sediment is produced while the oil is stored and this sediment may cause plugging of a filter or damage a pump.
There are several reasons for sediment being produced, one of which is considered to be the stability of asphaltene contained in heavy hydrocarbon oil. When asphaltene is surrounded by resin, the asphaltene is dispersed in heavy hydrocarbon oil without producing sediment. However, when resin is dissociated from asphaltene by hydrogenation and the balance between the asphaltene and the resin collapses, the asphaltene easily appears as sediment.